IHTMLDocument2::get_body fails in CHtmlView for IE 11

We've hit a simple, but critical, problem: IHTMLDocument2::get_body works in our embedded browser (CHtmlView) for IE7, but not IE11. We really want to start using the newer version, but this is a killer right now.

We use Visual Studio 2010. Native (unmanaged) C++. Problem occurs in both 32 and 64 bit builds. I don't know where this started failing (IE8? IE9? IE10?). OnNavigateComplete2 has fired before we try to call this function.

Here's our code, which has worked for us for a long time:

ComPtr<IHTMLTxtRange> CHighlightHTML::GetRange(ComPtr<IHTMLDocument2> document)
{
    ComPtr<IHTMLElement> elt;
    ComPtr<IHTMLBodyElement> body;

    if( SUCCEEDED(document->get_body(&elt.ReleaseGetValue())) )
        body = elt;

    if( body.IsValid() )
    {
        // Create a range from the entire body element.
        ComPtr<IHTMLTxtRange> range;
        CHECK_COM(body, createTextRange(&range.ReleaseGetValue()));
        return range;               
    }
}

But when we set the registry key: HKCU/Software/Microsoft/Internet Explorer/Main/FeatureControl/FEATURE_BROWSER_EMULATION

to 11000 for our .exe, then elt == NULL (so fails the body.IsValid() test)

If we have not set the registry key, or set the key to 7000 (so browser control is IE7), then it works again.

Help!